A variety of assays can be performed using an assay chip that includes one or more sensors positioned on a substrate. A cartridge can be employed to transport various liquids to the sensors. The cartridge typically includes one or more reservoirs that each holds one of the solutions. During the operation of the cartridge, the cartridge is inserted into a machine that causes the liquids in the reservoirs to be transported to the one or more sensors. The machine can then operate the one or more sensors so as to perform an assay on each of the sensors.
When the sensors are electrochemical sensors, the different liquids are delivered to each of the sensors in order to construct a test probe within a test volume that is positioned on the sensors. The different liquids include different components of the test volume including components of the test probe that bond to one another and/or to the sensor. Since it is desirable to perform different assays on different sensors, it is also desirable for the test probes built on different sensors to be different. As a result, cartridges for transporting the liquids to the sensors often include complex arrangements of channels and valves that introduce complexity, costs and inefficiencies into the system. As a result, there is a need for simplification of the process of performing multiple different assays on a sensor chip.